Process for surface treating aluminum and aluminum alloy articles

ABSTRACT

A process for surface treating aluminum and aluminum alloy articles is provided. The method includes the steps of providing a substrate of aluminum or aluminum alloy material, the substrate having an internal surface and an external surface; machining the external surface of substrate, thereby forming a first surface appearance on the external surface; forming a first oxide coating with a first color on the substrate surface by a first anodizing process; removing at least a portion of the first oxide coating on the internal surface of the substrate to make the substrate electricity conductive; machining the external surface of the substrate, thereby removing at least a portion of the first oxide coating on the external surface and forming a second surface appearance thereon; forming a second oxide coating with a second color on the area of the external surface excluding the first oxide coating by a second anodizing process.

BACKGROUND

1. Technical Field

The present disclosure relates to processes for surface treating aluminum and aluminum alloy articles.

2. Description of Related Art

Due to having many good properties such as light weight and quick heat dissipation, aluminum and aluminum alloy are widely used in making components (such as housings) of electronic devices. Aluminum and aluminum alloy are usually anodized to form an oxide coating thereon to acquire a decorative and wear resistant surface. When forming a multi-colored oxide coating, a typical anodizing and coloring process are repeatedly implemented. After one anodizing process, the subsequently colored area is exposed while the other area is shielded. However, the cost for providing the shielding is high. Moreover, it is difficult to achieve a precise and three-dimensional decorative pattern by this shielding.

Therefore, there is room for improvement within the art.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

An exemplary process for surface treating aluminum and aluminum alloy articles may include at least the following steps.

In a first step, an aluminum or aluminum alloy substrate is provided. The substrate includes an internal surface and an external surface.

In a second step, a first surface appearance of the external surface is formed by a first machining process. For example, the external surface may be sandblasted to achieve a dull surface appearance.

In a third step, the substrate is processed in a first anodizing process. The first anodizing process is carried out by dipping the substrate in an electrolytic bath containing sulfuric acid at a temperature of about 19-21° C., using a direct current in an approximate range from about 10 to 12 volts for about 45 to 55 minutes. The mass concentration of the sulfuric acid can be about 180 to 220 g/L (gram per liter), and is selected to be about 190-210 g/L in this embodiment. Therefore, a first oxide coating is formed on the internal and external surfaces of the substrate.

In a fourth step, the substrate is colored in a first dyeing process. Two alternative methods, i.e., chemical staining and adsorption staining may be used. Adsorption staining is implemented in this embodiment to color the first oxide coating. The first oxide coating presents a first color by this process.

In a fifth step, the colored substrate is processed in a sealing process to improve anti-contamination and anti-corrosion qualities of the first oxide coating.

In a sixth step, some portion or all of the first oxide coating on the internal surface of the substrate can be removed by a laser carving process to make the substrate electrically conductive.

In a seventh step, the external surface of the substrate is processed in a second machining process. By the second machining process, a portion or portions of the first oxide coating on the external surface is removed. The area of the external surface excluding the first oxide coating has a second surface appearance different from the first surface appearance. The second surface appearance can be textured differently than the first surface, such as a texture of line strips.

In an eighth step, the substrate is processed in a second anodizing process. The second anodizing process can be carried out by immersing the substrate into an electrolytic bath containing sulfuric acid at a temperature of about 19-21° C., using a direct current in an approximate range from about 9.5 to 10.5 volts for about 28 to 32 minutes. The mass concentration of the sulfuric acid can be about 180 to 220 g/L (gram per liter). A second oxide coating is formed on the area of the external surface excluding the first oxide coating.

In a ninth step, the substrate is colored in a second dyeing process. Two alternative methods, chemical staining and adsorption staining may be used. Adsorption staining is selected to color a second color on the second oxide coating.

In a tenth step, the colored substrate is processed in a sealing process to enhance anti-contamination and anti-corrosion qualities of the second oxide coating.

As the substrate is processed by two different machining and two different dyeing steps, the substrate can achieve two different anodized surface appearances with different colors.

It should be understood that the substrate can be pre-treated before the first anodizing process. The pre-treatment includes degreasing the substrate to remove oil stains on the substrate surface, immerging in a chemical polishing solution typically containing phosphoric acid and sulfuric acid, and then immerging in a solution containing about 20-40% (mass percent) nitric acid to remove the black coating on the substrate surface formed in the chemically polishing procedure.

It should be understood that the steps described in [0010] through [0014] can be repeated to obtain an aluminum or aluminum alloy article, which has an anodized surface with more than two different colors and more than two different surface appearances.

It should be understood that the steps described in [0010] can be omitted by painting ink e.g., to cover some portion or all of the internal surface of the substrate before the first anodizing process.

It should be understood, however, that even though numerous characteristics and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. 

1. A process for surface treating aluminum and aluminum alloy articles comprising: providing a substrate, the substrate being made of aluminum or aluminum alloy material, the substrate having an internal surface and an external surface; machining the external surface of the substrate, thereby forming a first surface appearance on the external surface; forming a first oxide coating on the whole substrate surface by a first anodizing process; dyeing a first color on the first oxide coating; removing at least a portion of the first oxide coating on the internal surface to make the substrate electrically conductive; machining the external surface of the substrate, thereby removing at least a portion of the first oxide coating on the external surface and forming a second surface appearance thereon; forming a second oxide coating on the area of the external surface excluding the first oxide coating by a second anodizing process; and dyeing a second color on the second oxide coating.
 2. The process for surface treating aluminum and aluminum alloy articles as claimed in claim 1, wherein the first surface appearance is a dull surface appearance formed by sandblasting.
 3. The process for surface treating aluminum and aluminum alloy articles as claimed in claim 2, wherein the second surface appearance is a texture of line strips.
 4. The process for surface treating aluminum and aluminum alloy articles as claimed in claim 1, wherein the first and second anodizing process are carried out in a electrolytic bath containing about 180-220 g/L sulfuric acid at a temperature of about 19-21° C.
 5. The process for surface treating aluminum and aluminum alloy articles as claimed in claim 4, wherein a direct current out in an approximate range from about 10 to 12 volts is used for about 45 to 55 minutes in the first anodizing process.
 6. The process for surface treating aluminum and aluminum alloy articles as claimed in claim 5, wherein a direct current in an approximate range from about 9.5 to 10.5 volts is used for about 28 to 32 minutes in the second anodizing process.
 7. The process for surface treating aluminum and aluminum alloy articles as claimed in claim 1, wherein a portion or all of the first oxide coating is removed form the internal surface of the substrate by a laser carving process.
 8. The process for surface treating aluminum and aluminum alloy articles as claimed in claim 1, further comprising a sealing process after the first and the second anodizing process.
 9. The process for surface treating aluminum and aluminum alloy articles as claimed in claim 1, wherein the dyeing process is an adsorption staining process.
 10. The process for surface treating aluminum and aluminum alloy articles as claimed in claim 1, further comprising before the first anodizing process, pre-treating the substrate by degreasing the surface of the substrate, chemically polishing the surface of the substrate and then removing the black coating on the substrate surface formed in the chemically polishing procedure.
 11. A process for surface treating aluminum and aluminum alloy articles comprising: providing a substrate, the substrate being made of aluminum or aluminum alloy material, the substrate having an internal surface and an external surface, the external surface having a first surface appearance thereon; forming a first oxide coating on the substrate surface by a first anodizing process; dyeing a first color on the first oxide coating; machining the external surface of the substrate, thereby removing at least a portion of the oxide coating on the external surface and forming a second surface appearance thereon; forming a second oxide coating on the area of the external surface excluding the first oxide coating by a second anodizing process; and dyeing a second color on the second oxide coating.
 12. The process for surface treating aluminum and aluminum alloy articles as claimed in claim 11, wherein the first surface appearance is formed by a first machining process.
 13. The process for surface treating aluminum and aluminum alloy articles as claimed in claim 12, wherein the first surface appearance is a dull surface appearance formed by sandblasting.
 14. The process for surface treating aluminum and aluminum alloy articles as claimed in claim 13, wherein the second surface appearance is a texture of line strips.
 15. The process for surface treating aluminum and aluminum alloy articles as claimed in claim 11, further comprising covering at least portions of the internal surface before the first anodizing step.
 16. The process for surface treating aluminum and aluminum alloy articles as claimed in claim 11, wherein at least portions of the internal surface is covered by ink.
 17. The process for surface treating aluminum and aluminum alloy articles as claimed in claim 11, further comprising a sealing process after the first and the second anodizing steps. 